fixed bug in mapvisualization.py

MapCanvas: used MapCanvasLayerModel that support lazy loading of QgsMapLayer instances
MapViews can have individual vector layer sources for overlay

minor changes

several updates to mapvisualization.py
cleanups + refactoring

added test/collapsibleGroupBox (idea: find a way to use QGIS resource icons without having QGIS started)

fixed icon of mainwindow

mapvisualization: fixed several optical issues, connected buttons

- added fileFilter to svg2png. if set, only files listed in svg2png.txt will be converted
- added updateInfoHTML
- prefers SVG instead PNG
- renamed png2qrc to file2qrc
- file2qrc add files without removing files already mentioned in the qrc

changen MapViewUI layout form horizontal to vertical
added MapView specific crosshairs

first steps to change MapViewCollection UI

virtualrasters.py - fixed setData(<vrt band name>)

removed frame lines from GUI